Measures to prevent terrorism have helped contribute to a surge in rat numbers in Paris, an expert told Euronews.

It's helpful for revealing the presence of bombs but much less so to protect against rats

Romain Lasseur
Pest control expert

Flooding in the river Seine, which has forced rodents out of their usual underground lairs has greatly increased sightings over the past month. But Romain Lasseur, who founded a pest control company after completing a PhD in toxicology, says the population has probably been on the increase for years thanks to changing habits in the French capital.

Combined with more people picnicking in parks and leaving food on the streets, the disappearance of dustbins following the spate of terrorist attacks in 2015 has given rats easier access to food sources, he claimed.

"These food resources are not properly protected like we see with public dustbins been replaced with simple plastic bags as a result of the security plan [initiated in 2015]," he said. "It's helpful for revealing the presence of bombs but much less so to protect against rats. We're simplifying the environment to their advantage."

Lasseur points out that it is almost impossible to calculate the number of rats in Paris - estimates vary between two and six million - but with plenty of food available and warmer winters cutting mortality rates, there are fewer natural brakes on their growth.

In two years, a single mating pair of rats can create a colony of more than 45,000 as females are capable of breeding four times a year, with around eight offspring per litter.

Furthermore, reluctance to use poison to control the population has meant that the problem has been growing, unseen, Lasseur says:

"This urban benevolence leads to not controlling the populations when they don't cause a problem but when numbers explode, it's too late."

Lasseur says the city needs to take a more aggressive and consistent approach to pest control including fining people who leave out food that rats can access.

"It needs political courage to do that, but what else can we do, let rats multiply like this on our streets? Is that how we want people to see our country?"